The invention herein is concerned with the die casting of metal in which molten metal is forced into metallic molds under pressure. Conventionally such pressure is provided by hydraulic means effected by utilizing a mechanically actuated piston or ram acting on the molten metal itself.
The invention herein does not use hydraulic pressure but instead utilizes the pressure produced by steam or other vapor preferably generated within the molding die itself in a manner to be described.
In the present state of the technology of die casting the apparatus utilized for forcing the molten metal into the molds includes a hydraulic ram. The ancillary apparatus needed for operating the ram includes pumps, cylinders and associated equipment. In a so-called die casting machine, all of the apparatus is included making the device large and costly.
Hydraulically operated die casting machines are subject to disadvantages most of which are traceable directly to the method of forcing the molten metal into the molds. These disadvantages are inordinate die wear, excessive flash in the castings, need for robust dies and inability to make delicate and thin-walled castings. Probably the principal reason for these disadvantages is that the plunger type injection system requires a fast-moving ram which tends to blow the die open and stress the same.
The advantages of the vapor cast method and apparatus which will be described point out other areas of the conventional system which are not desirable but have been tolerated because they are inherent in the use of the plunger type injection system.
Besides the elimination of all of the hydraulic mechanisms, vapor casting apparatus can be made much smaller than the conventional injection type die casting machines for the same size of molds which results in considerable economy.
Die cooling systems are not as essential because in the vapor casting method the heat from the metal is absorbed in providing steam vapor energy.
The vapor casting apparatus is preferably arranged to be operated vertically thereby saving considerable floor space. Plunger type injection molding systems as used today are practically all horizontal.
Other mechanical advantages are related to simpler and more economical construction of the vapor casting machine.
The prior art which is known to the applicants and which relates to the use of applying pressure to molds in casting metal is generally concerned with attempting to compact the casting and eliminate blow holes by the use of water, steam or compressed air. Steam or compressed air has been used to cause the metal of a pot or ladle to flow through a conduit into a mold.
U.S. Pat. No. 8,427 issued to Jones shows the use of a mold in which there is a large ingot to be formed. The ingot mold is filled partway and then steam is admitted to the mold. Mention is also made of spraying water into the jacket of the mold. U.S. Pat. No. 464,441 issued to Rockman also teaches the use of compressed air or steam on castings to compress them.
In neither of these prior art patents is there an injection of a specific volume of water or other varporizable material into a body of molten metal within the die or adjacent to the die to produce steam or other vapor which forces the metal to flow from the well containing the body of molten metal through the gating channels and into the molding cavities themselves.
The next patent of the prior art which is of interest is U.S. Pat. No. 1,092,934 issued to Mellen in which there is a crucible that is maintained at high heat within a furnace and that is provided with an extrusion die in its bottom below the body of metal. Water, oil, etc., is admitted into the top of the crucible to expand and exert a constant gaseous pressure on the surface of the molten metal to force it through the die in the bottom of the crucible.
The prior art as known does not inject a metered quantity of water or other vaporizable material into the center of a body of molten metal that is contained in a well formed in or adjacent to a die set while the die set is in fully closed condition whereby the vapor generated continuously expands and forces the metal from the well into the mold cavities by way of the gating channels. The expanding steam or other vapor thus draws heat for its energy from the molten metal that surrounds it.